The present invention relates generally to semiconductor manufacturing, and more particularly to a gauge and method for counting accurately and efficiently a number of leadframes residing in a leadframe carrier or magazine.
Integrated semiconductor devices are typically constructed xe2x80x9cen massexe2x80x9d on a wafer of silicon. Each device generally takes the form of an integrated circuit (IC) die, which is bonded to the die-mounting pad of a leadframe. The wire attachment pads on the die are connected with their corresponding leads on the leadframe typically with aluminum or gold wire during a wire bonding process. The die and leadframe are then encapsulated in a plastic or ceramic package, which is then recognizable as an IC xe2x80x9cchipxe2x80x9d. Since nine or more leadframes are typically interconnected as a leadframe strip during the manufacturing process, a trim and form operation separates the individual chips from the leadframe strip and forms (bends) the leads of the chip into the required configuration. IC chips come in a variety of forms such as microprocessors, dynamic random access memory (DRAM) chips, static random access memory (SRAM) chips, flash memory chips, gate arrays, etc. The chips are interconnected in myriad combinations on printed circuit boards, along with other types of discrete components such as resistors and capacitors, by any number of techniques, such as socketing and soldering.
An example of a typical leadframe strip is depicted in FIG. 1, and designated at reference numeral 10. From the point in the manufacturing process where the pads 11 of a leadframe strip are coated with adhesive prior to die bonding until the point where the individual chips are separated from the leadframe strip rails 12 during a trim and form process, the leadframe strip 10 is treated as a single unit in the manufacturing process. Automatic handling machinery is designed to retrieve the partially complete leadframe strip assemblies from leadframe storage devices commonly called leadframe carriers or magazines. One type of prior art leadframe strip carrier is depicted in FIG. 2, and designated at reference numeral 20. The interior of the carrier 20 has a pair of opposed mirror-image grooved faces 22. Each groove on one face and its mirror-image groove on the opposing face acts as a slot into which a single lead frame strip 10 may be inserted. The carrier 20 of FIG. 2, for example, is capable of supporting twenty-seven leadframe strips. This prior art leadframe strip carrier suffers from two drawbacks: high cost of manufacture and inconvenient design.
The leadframe strip carrier of prior art FIG. 2 is expensive, for example costing up to about $250 per unit. This cost is especially significant considering that a semiconductor manufacturer may need several thousand carriers of various sizes, and since the carriers are subject to damage and wear during the semiconductor manufacturing process, they are not expected to last much more than a single year.
Another form of leadframe carrier or magazine is illustrated in FIGS. 3a-3d, and is designated at reference numeral 30. The leadframe carrier 30 has several advantages over the carrier 20 of prior art FIG. 2. The leadframe carrier 30 has a generally flat bottom portion 32 and C-shaped side portions 34 and 36, respectively, which collective work to contain a stack of leadframes 38 therein (see, e.g., FIG. 3c). The carrier 30 does not have the high precision grooves of carrier 20; consequently the insertion and removal of leadframes from the carrier 30 is relatively simple. Furthermore, the structure of the carrier 30 makes production of the carrier relatively inexpensive and a single type of carrier 30 may be utilized for multiple types of leadframe strips.
Because of the advantages associated with the leadframe carriers 30 of FIGS. 3a-3d, such leadframe carriers are commonly used in semiconductor back-end manufacturing to carry the leadframe strips from one process to another, for example, from mold to post-mold cure, solder plating, trim and form processes, etc. One full carrier of SOIC44 leadframe strips contains, for example, 120 strips. The number of leadframe strips contained within the leadframe carrier need to be known and thus counted in at least the following events: (1) to identify the number of strips residing in a partial (last) carrier of a production lot, (2) to identify the number of strips within a carrier in the event that leadframe strips are transferred from one carrier to another, and (3) to identify the number of remaining strips within the leadframe carrier to confirm the proper number of strips after a machine jams or another xe2x80x9chick-upxe2x80x9d occurs in the process.
Normally, strips 10 in the leadframe carriers 30 are counted manually using a pointer or a pair of tweezers, as illustrated in FIG. 3d. Such manual counting is a time consuming process, for example, taking an average of 60 seconds per carrier (not including recounts). In addition, the manual counting method is prone to errors. Clearly, there is a need in the art for a system and method of accurately and efficiently determining the number of leadframe strips within a leadframe carrier or magazine.
The present invention relates to a system and method for accurately and efficiently determining a number of leadframe strips within a leadframe carrier or magazine.
According to the present invention, a leadframe strip counting gauge and a method of counting leadframes using such a gauge is disclosed. The leadframe strip counting gauge comprises an elongate member having a lateral edge that contains a series of periodic variations such as notches thereon. The periodic variations generally coincide with the spatial period of the leadframes when stacked within the leadframe carrier. The gauge further comprises leadframe count indicia such as numbers associated with the elongate member which coincide generally with the periodic variations. The gauge may be used to count the number of leadframes within the leadframe carrier by placing the gauge near or in contact with the leadframe carrier such that the lateral edge is near or abuts the stack of leadframes therein. By evaluating the leadframe count indicia associated with the gauge and the leadframe stack near the indicia, an accurate leadframe count may be achieved in an efficient manner.
According to one aspect of the present invention, a leadframe strip counting gauge comprises a gauge member having an engagement portion which is adapted for subsequent association with a leadframe carrier having leadframes contained therein. The gauge further comprises leadframe count indicia associated with the gauge member. The leadframe count indicia may be spatially distributed with respect to the gauge member and is adapted to provide a count representing the number of leadframes residing within the leadframe carrier.
According to another aspect of the present invention, the engagement portion of the gauge member comprises a periodically varying lateral edge having a spatial period which coincides generally with a spatial period of the leadframes as stacked in the leadframe carrier or magazine. Further, the periodically varying lateral edge may constitute notches formed therein, and when the gauge is brought into contact with the stacked leadframes, the periodically varying lateral edge engages the leadframes such that each leadframe strip engages a separate lateral edge variation, respectively.
According to yet another aspect of the present invention, each notch associated with the gauge member comprises a first and second angled edge, respectively. The first angled edge exhibits a positive slope while the second angled edge exhibits a negative slope; and the angled edges intersect one another to form a trough. The angle formed between the first angled edge and a plane perpendicular to the gauge length positioned at the trough is about 10 degrees and the angle formed between the second angled edge and the same plane is about negative 10 degrees, respectively.
According to still another aspect of the present invention, a method of counting leadframes residing in a leadframe carrier comprises positioning a leadframe counting member near a leadframe carrier containing leadframes therein. The method further comprises the step of determining the number of leadframes in the leadframe carrier using leadframe count indicia associated with the leadframe counting member.
According to another aspect of the present invention, a method of counting leadframes residing in a leadframe carrier comprises generally abutting the leadframe counting member against the leadframe carrier such that an engagement portion of the counting generally contacts the leadframes stacked within the leadframe carrier. The engagement portion may comprise a periodically varying lateral edge having a spatial period which generally coincides with a spatial period of the stacked leadframes such that each leadframe engages individually a variation associated with the lateral edge of the counting member.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
FIG 1 is a prior art plan view of a leadframe strip employed in back-end semiconductor processing;
FIG. 2 is a prior art perspective view illustrating an extruded leadframe carrier used to transport leadframe strips between various process stations during back-end semiconductor processing;
FIG. 3a is a prior art front view of another form of leadframe carrier or magazine used to transport leadframe strips between various process stations during back-end semiconductor processing;
FIG. 3b is a cross section of a leadframe carrier of FIG. 3a taken along dotted line 3b xe2x80x943b thereof, and illustrating a body portion of the carrier used for storing and transporting leadframes strips in back-end semiconductor processing;
FIG. 3c is a perspective view of the leadframe carrier of FIG. 3a illustrating the leadframe carrier having an undetermined number of leadframe strips residing therein;
FIG. 3d is a perspective view of the leadframe carrier of FIG. 3a illustrating a prior art method of counting the undetermined number of leadframes residing within the leadframe carrier using a pointer type apparatus and individually counting the leadframe strips;
FIG. 4a is a side view of a leadframe strip counting gauge for counting leadframe strips residing within a leadframe carrier or magazine according to the present invention;
FIG. 4b is a fragmentary side view illustrating a portion of the lateral edge of the leadframe strip counting gauge according to an exemplary aspect of the present invention;
FIG. 5 is a perspective view of the leadframe carrier of FIG. 3a, wherein a leadframe strip counting gauge is utilized to count the leadframe strips residing therein according to one exemplary aspect of the present invention, and
FIG. 6 is a flow chart illustrating a method of counting leadframes within a leadframe carrier using a leadframe counting mechanism such as the leadframe strip counting gauge of FIG. 4 according to the present invention.